I see a lot of the pros doing this. The 5'9 guys riding a 52cm with a 130mm stem or a 6'2 guy doing the same on a 56cm.

I ask, why?

I understand there is weight savings and the head tube is shorter for a slightly more aggressive geometry, but isn't that at the cost of less control? I've always heard the longer the stem the less control you have when you turn. So, for those pros taking the crazy descends and sharp 90 degree turns at a km out, it would seem advantageous to ride a frame that fits them and go with the shorter stem.

Few things.

I'm 5'9"/175cm and ride a 52 (53cm top tube), with a 12 cm stem. It fits perfectly. (getting into the drops was tricky when i was up at 85 kilos, i've lost weight now, and it's easy.)Most of steering a bike is leaning it, not heaving on the bars. Moving the bars too much potentially makes the bike less stable and controllable.Fashionable mountain bikers use tiny stems and massive bars to get down descents no faster than a good rider can get down with 600mm bars and a 12 cm stem. Its partly driven by the mega slack head angles they use to be freeridey and gnar, using a long stem on a 67 head angle is a "bit of a bad idea". I don't know where the read across into road came from.

Moving the saddle back to create an effectively longer top tube (assuming equal seat tube angle) changes the rider's position relative to the pedals, which changes the rider's muscle use and ability to spin the pedals. It also changes the rider's weight distribution on the bike which affects handling. I think it's a bad idea to make those changes away from the rider's ideal just to fit a frame. Better to buy a frame with an appropriate ETT length.

Also going down a "gnarly" mountain hill with a 12cm stem and narrow straight bars spells instant OTB (over the bar) wipeout... You are not a good rider if you manage this at speed, you've got world class rider written all over yourself...

Or... the hill wasn't that gnarly to begin with.

The reason to go short stem with wide bars (75cm+) is because steering with wide bars and long stem is like pushing a tug boat... wider bars slow the steering down, but they also provide more leverage and this is the key feature.

which is where 99% of the riders shouting about short stems being better come unstuck. Cos they really don't know what they are doing. Those who do will ride just about anything. Short, wide, narrow, long. Probably where the cross over into the road scene has come from, nodders shouting about short, good, long, bad.

Long stem is the way to go as long as you can get enough saddle height from the small frame. I'm 6'4" and ride a 58 with 130mm stem, perfect - no twitch. My saddle height is pretty maxed out though on my s-works with sloping tt. Dying for a non-sloping C59 or C-dale Evo next.

This discussion should also consider body proportions. Some have loooong legs and short torso, some have chimp legs and long torsos and arms. Fit is hard to discuss on a forum.

Well no, it's basic physics. When the terrain tries to knock your wheels off your intended line, that is about every 15-20 centimeter on a mountainbike trail, and on roadbikes never unless you hit a pothole, then wider bars provide more leverage and thus more control. The short stems are because you can't ride wide bars with tall stems. Really, try it, it's the strangest feeling ever.

Get over the 'problem-with-posers'-attitude, it's just a matter of what is practical...

How much steering are you really doing in the corners. Not much I hope. If you are you are not descending well.

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Moving the saddle back to create an effectively longer top tube (assuming equal seat tube angle) changes the rider's position relative to the pedals, which changes the rider's muscle use and ability to spin the pedals. It also changes the rider's weight distribution on the bike which affects handling. I think it's a bad idea to make those changes away from the rider's ideal just to fit a frame. Better to buy a frame with an appropriate ETT length.

+1. Seatpost setback is required if you have extraordinarily long legs, and you need that extra length to get your knees in the right spot; i.e. over the spindle when the pedal is at the forward position.

prefer longer frames with shorter stems. Problem being, the head tubes tend to be taller than I would like. It makes riding a stock "modern" bike quite difficult. Most bikes with a 55 top tube have a 160 head tube. Not all obviously, but most.

Moving the saddle back does not necessarily change the relationship between the bottom bracket, only if it is changed in isolation. This is not what happens with a properly set-up bike, hence the long stems. That is also why you should use a Fit-Stik, or similar device, to set-up your bikes. From the bottom bracket, the rest of your dimensions flow.

Also not sure why mtb setups got into this thread. Of course in the woods you want wider bars and short stems with slack angles the more gnar and steep the trail gets.

In this case its because i'm pretty sure it's where the "everyone knows short stems give better handling" came from. And if everyone says it often enough, it becomes true, much like the roadie maxim, "narrow tyres pumped up rocks solid are fastest". Which is only true if you are riding on mirror smooth surfaces (essentially a velodrome), so again, a very small subset, and a very small advantage.

[quote="Geoff"]Moving the saddle back does not necessarily change the relationship between the bottom bracket, only if it is changed in isolation. /quote]

Yes, in a way that is true. Imagine rotating the rider's position forward on the bike using the BB as the axis (moving the set and bars forward). His position vs the BB does not change, and the position vs the seat and bars do not change if they are moved the correct amount. However, his position on the bike does change- he's farther forward. But since we're on a planet with gravity, this puts more of the rider's weight on the front of the bike and the rider has to support more of his weight on his arms. If he's rotated too forward he will be using more upper body muscles just to maintain positon on the bike. (see https://www.stevehoggbikefitting.com/bl ... oad-bikes/ for a much better explanation)

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